As an imaging apparatus, a pinhole camera is well-known. According to the pinhole camera, a subject image is formed on a photosensitive material such as a film in a dark box through a hole, called a pinhole, formed on one plane of the dark box. In the case of the pinhole camera, slight light passing through the pinhole reaches one point on the photosensitive material. Therefore, the amount of light is small. In image capturing under low light conditions, the pinhole camera is of little practical use.
Accordingly, a conventional common imaging apparatus includes an imaging lens 101. As shown in FIG. 6, the apparatus has a structure in which an imaging device 102 is arranged in the focal position of the imaging lens 101. Image light from a subject captured by the imaging lens 101 is subjected to optical processing through an optical system 103 so that the imaging device 102 converts the light into electric signals. An image is formed on the image surface of the imaging device 102. Electric signals that are produced from the subject image on the image surface by photoelectric conversion through the imaging device 102 are subjected to predetermined signal processing through a signal processing circuit 104 arranged downstream of the imaging device 102.
This type of imaging apparatus has been used by itself as a digital still camera. In addition, the imaging apparatus has recently been being incorporated into compact portable devices such as mobile phones. Reducing the size, weight, and cost of the imaging apparatus is desired in incorporating the apparatus into a mobile phone. In other words, the use of a small-sized, lightweight, and low-cost imaging apparatus contributes to the reduced size, weight, and cost of a compact portable device such as a mobile phone.
In the imaging apparatus using the imaging lens 101, however, the size of the apparatus is increased by the amount corresponding to the size of the imaging lens 101, the weight thereof is increased by the amount corresponding to the weight of the imaging lens 101, and further, the cost thereof is increased by the amount corresponding to the cost of the imaging lens 101. In addition, the amount of ambient light is reduced due to shading of the imaging lens 101. In shooting a subject with a wide dynamic range, the difference in signal charge between pixels of the imaging device 102 is large. Therefore, it is desired to design the imaging device 102 so as to provide a wide dynamic range.
Methods and devices consistent with the present invention are made in consideration of the above problems and to provide an imaging apparatus which does not need the conventional lens, thereby achieving a reduction in size, weight, and cost.